Hans Reichenbach
Relativity shows that even the basic principles of physics can be revised; what science can justify is a probability, and how a theory was found is a different question from whether it holds.
Placement
Leader of the Berlin Group of logical empiricism, from 1938 in Los Angeles: a philosophy of space, time and probability built on relativity theory, a pragmatic justification of induction, and the distinction between the context of discovery and the context of justification.
Key ideas
- Revisable a priori (principles of coordination)
- Frequency theory of probability
- Pragmatic justification of induction
- Context of discovery vs. context of justification
Teachers: David Hilbert, Ernst Cassirer
Students: Carl Gustav Hempel, Hilary Putnam
Influence
Influenced by 3
David Hilbert studied with
studied with
Reichenbach studied mathematics with Hilbert in Göttingen as part of studies that also took him to Cassirer, Planck and Sommerfeld; his doctorate (Erlangen, 1915) was taken elsewhere. Course attendance, not supervision. SEP “Hans Reichenbach”
Evidence: AI draft
David Hilbert › 1862–1943
Ernst Cassirer studied with
studied with
Reichenbach studied physics, philosophy and mathematics in Berlin, Munich and Göttingen with, among others, Cassirer, Planck, Sommerfeld and Hilbert; his doctorate (Erlangen, 1915) was accepted by Paul Hensel, not Cassirer. Course attendance, not supervision. SEP “Hans Reichenbach”
Evidence: AI draft
Ernst Cassirer › 1874–1945
Albert Einstein
influenced by
Reichenbach, who heard Einstein’s Berlin lectures on relativity, recast Kant’s a priori as revisable coordinating principles (1920) and analysed distant simultaneity as a matter of definition (1928). H. Reichenbach, Relativitätstheorie und Erkenntnis apriori (1920); Philosophie der Raum-Zeit-Lehre (1928); SEP “Hans Reichenbach”
Evidence: AI draft
Albert Einstein › 1879–1955
Influenced 2
Carl Gustav Hempel taught
taught
Hempel studied with Reichenbach in Berlin from 1929, went to Vienna that autumn at his suggestion and belonged to his Berlin Group; after Reichenbach’s emigration his doctorate on probability (1934) was examined by Wolfgang Köhler and Nicolai Hartmann. SEP “Carl Hempel”
Evidence: also in InPhO · InPhO
Carl Gustav Hempel › 1905–1997
Hilary Putnam taught
taught
Putnam took his PhD at UCLA in 1951 under Reichenbach with a dissertation on the meaning of the concept of probability in application to finite sequences. H. Putnam, The Meaning of the Concept of Probability in Application to Finite Sequences (diss. UCLA 1951; printed 1990)
Evidence: also in InPhO · InPhO
Hilary Putnam › 1926–2016
Criticism
Criticized by 1
Karl Popper
criticised by
Popper rejected Reichenbach’s probability logic of induction: no principle of induction can be justified without infinite regress, and hypotheses cannot be assigned probabilities (Logik der Forschung, 1934). K. Popper, Logik der Forschung (1934), §§ 1, 80–81; H. Reichenbach, Wahrscheinlichkeitslehre (1935)
Evidence: AI draft
Karl Popper › 1902–1994
Criticizes 1
Immanuel Kant
criticised
Reichenbach argued that relativity theory is incompatible with Kant’s synthetic a priori of Euclidean space, keeping only a revisable, constitutive a priori (Relativitätstheorie und Erkenntnis apriori, 1920). H. Reichenbach, Relativitätstheorie und Erkenntnis apriori (1920); SEP “Hans Reichenbach”
Evidence: AI draft
Immanuel Kant › 1724–1804
Works
Relativity theory against Kant: physics needs principles that coordinate mathematics with experience, but they are not fixed for all time.
Meaning and knowledge in terms of probability, the pragmatic justification of induction, and the separation of discovery from justification.
Position
Reichenbach began as a Kantian and used relativity against Kant. In 1920 he separated two meanings of the a priori: necessary and unrevisable, and constitutive of the object of knowledge. Physics needs principles that coordinate its mathematics with reality, but relativity had shown that such principles can change; so they are constitutive but revisable, and after Moritz Schlick’s criticism he soon called them conventions. In The Philosophy of Space and Time (1928) he argued that the geometry of physical space becomes an empirical question only once a coordinating definition, for instance of a rigid rod, has been fixed. He interpreted probability as the limit of relative frequency in a sequence of events and gave induction a pragmatic justification: if any method can find such limits, the simple inductive rule will, though it offers a “posit”, not a guarantee. Experience and Prediction (1938) made a distinction that became standard: philosophy of science reconstructs the context of justification and leaves the context of discovery to psychology. His analysis of tense by speech time, event time and reference time (1947) is still used in linguistics; The Direction of Time (1956) introduced the principle of the common cause. Karl Popper rejected any probabilistic logic of induction, and Reichenbach answered that falsification itself needs probabilities. Thomas Kuhn, Paul Feyerabend and the sociology of science later questioned whether discovery and justification can be separated so cleanly.
Life & context
Hans Reichenbach was born in Hamburg on 26 September 1891. He studied civil engineering in Stuttgart, then physics, mathematics and philosophy in Berlin, Munich and Göttingen; among his teachers were Ernst Cassirer, Max Planck, Arnold Sommerfeld and David Hilbert. He took his doctorate at Erlangen in 1915 with a thesis on probability. In Berlin he attended Albert Einstein’s lectures on relativity and became his friend. In 1920 he qualified as a lecturer at the Technische Hochschule Stuttgart with The Theory of Relativity and A Priori Knowledge. In 1926, with Einstein’s support, he was appointed to teach natural philosophy at the University of Berlin, where the Society for Empirical Philosophy became the centre of the “Berlin Group” with Kurt Grelling, Walter Dubislav and others; from 1930 he edited the journal Erkenntnis with Rudolf Carnap. Dismissed in 1933 under the Nazi laws, he taught at the new University of Istanbul until 1938, then at the University of California, Los Angeles. Carl Gustav Hempel studied with him in Berlin, Hilary Putnam and Wesley Salmon took their doctorates with him in Los Angeles. He died there on 9 April 1953.
Further main works
- The Philosophy of Space and Time (Philosophie der Raum-Zeit-Lehre, 1928)
- The Theory of Probability (Wahrscheinlichkeitslehre, 1935)
- Philosophic Foundations of Quantum Mechanics (1944)
- Elements of Symbolic Logic (1947)
- The Rise of Scientific Philosophy (1951)
- The Direction of Time (posthumous, 1956)
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